Technology: 19th-century engine refrigerates without CFCs

A HEAT PUMP cycle invented in 1816 forms the basis of a new cooling unit for domestic refrigerators that is entirely free of chlorofluorocarbon (CFC) refrigerants. CFCs harm the Earth's stratospheric ozone layer.

The cooling unit, developed by Sunpower of Athens, Ohio, uses only the inert gas helium as a working fluid. Production models could be more efficient than normal refrigerators, says David Berchowitz, design engineer on the project.

Robert Stirling, a Scottish clergyman and inventor, devised the principle of the Stirling cycle. The cycle can be used as an engine, driven by heat produced external to the engine itself, or it can be used as a heat pump, driven by mechanical energy. During much of the nineteenth century, the Stirling engine competed with the steam engine, until they were both superseded by the internal combustion engine around the turn of the century.

Interest in the Stirling cycle did not ...

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